Work machine, system, and method of controlling work machine

ABSTRACT

A payload calculation value (CalcuPayload) of a load within a bucket is calculated based on load of a boom cylinder. An amount of change per unit time in information on at least one of an operation command value for operating the boom cylinder and a speed of extension and contraction of the boom cylinder is sensed. A payload value is determined by correcting based on the amount of change per unit time, the payload calculation value (CalcuPayload) obtained by calculation.

TECHNICAL FIELD

The present disclosure relates to a work machine, a system, and a method of controlling a work machine.

BACKGROUND ART

A load within a bucket is important for knowing a workload of a work machine. For example, Japanese Patent Laying-Open No. 2010-89633 (PTL 1) and WO2018/087834 (PTL 2) each disclose a technique for calculating a payload value of a load within a bucket.

In PTL 1, a current payload value of a load is obtained by calculation, based on a posture of a work machine and a pressure applied to a boom cylinder. By integrating the current payload value, an integrated payload value is calculated. When the integrated payload value attains to a target payload value, an operator is notified of that state.

In PTL 2, a payload value of a load within a bucket is corrected based on an acceleration in extension and contraction of a boom cylinder. An error caused by inertia of a work implement based on an operation of a boom, an arm, a bucket, and the like can thus be eliminated from the payload value and measurement accuracy in measurement of a load can be improved.

CITATION LIST Patent Literature

-   PTL 1: Japanese Patent Laying-Open No. 2010-89633 -   PTL 2: WO2018/087834

SUMMARY OF INVENTION Technical Problem

In works for excavating soil with a work machine such as a hydraulic excavator and loading soil onto a dump truck, a carrying capacity should be equal to or lower than a maximum carrying capacity of the dump truck. As a plurality of times of excavation and a plurality of times of loading onto the dump truck are performed, an operator is notified of a carrying capacity calculated by measuring an amount of soil loaded each time and summing the amounts. In order to measure an amount of soil each time, an angle of the boom, the arm, and the bucket of the work implement and a hydraulic pressure of the boom cylinder are required. Therefore, a sensor is attached to measure an amount of soil in the bucket during a boom raising operation after soil is excavated and loaded in the bucket.

A boom cylinder pressure during the raising operation varies (pulsates) as the boom is operated. Therefore, it is difficult to accurately measure a load.

An object of the present disclosure is to provide a work machine, a system, and a method of controlling a work machine that allow improvement in accuracy in measurement of a load.

Solution to Problem

A work machine in the present disclosure includes a boom, an arm, a bucket, a boom cylinder, and a controller. The arm is attached to a tip end of the boom. The bucket is attached to a tip end of the arm. The boom cylinder drives the boom. The controller calculates a payload calculation value of a load within the bucket based on load of the boom cylinder, detects an amount of change per unit time in information on at least one of an operation command value for operating the boom cylinder and a speed of extension and contraction of the boom cylinder, and determines a payload value by correcting based on the amount of change per unit time, the payload calculation value obtained by calculation.

Advantageous Effects of Invention

According to the present disclosure, a work machine, a system, and a method of controlling a work machine that allow improvement in accuracy in measurement of a load can be achieved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram schematically showing a construction of a work machine in one embodiment of the present disclosure.

FIG. 2 is a block diagram showing a schematic configuration of a system of the work machine shown in FIG. 1.

FIG. 3 is a diagram showing a functional block within a controller shown in FIG. 2.

FIG. 4 is a flowchart showing a method of controlling the work machine in one embodiment of the present disclosure.

FIG. 5 is a diagram showing change over time in PPC pressure of a boom, amount of change in PPC pressure of the boom, and payload calculation value (CalcuPayload).

DESCRIPTION OF EMBODIMENTS

An embodiment of the present disclosure will be described below with reference to the drawings.

The same or corresponding components in the specification and the drawings have the same reference characters allotted and redundant description will not be repeated. In the drawings, a feature may not be shown or simplified for the sake of convenience of illustration.

The present disclosure is applicable to a work machine other than a hydraulic excavator so long as the work machine includes a boom, an arm, and a bucket. In the description below, “up”, “down”, “front”, “rear”, “left”, and “right” refer to directions with an operator seated in an operator's seat 2 b within an operator's cab 2 a being defined as the reference.

<Construction of Work Machine>

FIG. 1 is a side view schematically showing a construction of a hydraulic excavator as an exemplary work machine in one embodiment of the present disclosure. As shown in FIG. 1, a hydraulic excavator 100 in the present embodiment mainly includes a travel unit 1, a revolving unit 2, and a work implement 3. A work machine main body is constituted of travel unit 1 and revolving unit 2.

Travel unit 1 includes a pair of left and right crawler belt apparatuses 1 a. Each of the pair of left and right crawler belt apparatuses 1 a includes a crawler belt. As a pair of left and right crawler belts is rotationally driven, hydraulic excavator 100 travels.

Revolving unit 2 is provided as being revolvable with respect to travel unit 1. Revolving unit 2 mainly includes operator's cab (cab) 2 a, operator's seat 2 b, an engine compartment 2 c, and a counterweight 2 d. Operator's cab 2 a is arranged, for example, on the forward left (on a front side of a vehicle) of revolving unit 2. Operator's seat 2 b where the operator takes a seat is arranged in an internal space in operator's cab 2 a.

Each of engine compartment 2 c and counterweight 2 d is arranged in a rear portion (on a rear side of the vehicle) of revolving unit 2 with respect to operator's cab 2 a. An engine unit (an engine and an exhaust treatment structure) is accommodated in engine compartment 2 c. An engine hood covers the top of engine compartment 2 c. Counterweight 2 d is arranged in the rear of engine compartment 2 c.

Work implement 3 is pivotably supported on the front side of revolving unit 2, and for example, on the right of operator's seat 2 a. Work implement 3 includes, for example, a boom 3 a, an arm 3 b, a bucket 3 c, a boom cylinder 4 a, an arm cylinder 4 b, and a bucket cylinder 4 c. Boom 3 a has a base end pivotably coupled to revolving unit 2 with a boom foot pin 5 a being interposed. Arm 3 b has a base end pivotably coupled to a tip end of boom 3 a with a boom tip end pin 5 b being interposed. Bucket 3 c is pivotably coupled to a tip end of arm 3 b with a pin 5 c being interposed.

Boom 3 a can be driven by boom cylinder 4 a. As a result of this drive, boom 3 a can pivot around boom foot pin 5 a in an upward/downward direction with respect to revolving unit 2. Arm 3 b can be driven by arm cylinder 4 b. As a result of this drive, arm 3 b can pivot around boom tip end pin 5 b in the upward/downward direction with respect to boom 3 a. Bucket 3 c can be driven by bucket cylinder 4 c. As a result of this drive, bucket 3 c can pivot around pin 5 c in the upward/downward direction with respect to arm 3 b. Work implement 3 can thus be driven.

Work implement 3 includes a bucket link 3 d. Bucket link 3 d includes a first link member 3 da and a second link member 3 db. A tip end of first link member 3 da and a tip end of second link member 3 db are coupled to each other as being pivotable relative to each other with a bucket cylinder top pin 3 dc being interposed. Bucket cylinder top pin 3 dc is coupled to the tip end of bucket cylinder 4 c. Therefore, first link member 3 da and second link member 3 db are coupled to bucket cylinder 4 c with the pin being interposed.

First link member 3 da has a base end pivotably coupled to arm 3 b with a first link pin 3 dd being interposed. Second link member 3 db has a base end pivotably coupled to a bracket at a root of bucket 3 c with a second link pin 3 de being interposed.

A pressure sensor 6 a is attached to a head side of boom cylinder 4 a. Pressure sensor 6 a can detect a pressure (a head pressure) of hydraulic oil within a cylinder-head-side oil chamber 40A of boom cylinder 4 a. A pressure sensor 6 b is attached to a bottom side of boom cylinder 4 a. Pressure sensor 6 b can detect a pressure (a bottom pressure) of hydraulic oil within a cylinder-bottom-side oil chamber 40B of boom cylinder 4 a.

Stroke sensors (sensing units) 7 a, 7 b, and 7 c are attached to boom cylinder 4 a, arm cylinder 4 b, and bucket cylinder 4 c, respectively.

A boom angle θb can be calculated from an amount of displacement of a cylinder rod 4 ab with respect to a cylinder 4 aa in boom cylinder 4 a. An arm angle θa can be calculated from an amount of displacement of a cylinder rod in arm cylinder 4 b.

A bucket angle θk can be calculated from an amount of displacement of a cylinder rod in bucket cylinder 4 c.

Potentiometers 9 a, 9 b, and 9 c may be attached around boom foot pin 5 a, boom tip end pin 5 b, and pin 5 c, respectively. Boom angle θb can be calculated from a measurement value from potentiometer 9 a. Arm angle θa can be calculated from a measurement value from potentiometer 9 b. Bucket angle θk can be calculated from a measurement value from potentiometer 9 c.

Inertial measurement units (IMUS) 8 a, 8 b, 8 c, and 8 d are attached to revolving unit 2, boom 3 a, arm 3 b, and first link member 3 da, respectively. IMU 8 a measures an acceleration of revolving unit 2 in a fore/aft direction, a lateral direction, and the upward/downward direction and an angular acceleration of revolving unit 2 around the fore/aft direction, the lateral direction, and the upward/downward direction. IMUS 8 b, 8 c, and 8 d measure accelerations of boom 3 a, arm 3 b, and bucket 3 c in the fore/aft direction, the lateral direction, and the upward/downward direction and angular accelerations of boom 3 a, arm 3 b, and bucket 3 c around the fore/aft direction, the lateral direction, and the upward/downward direction, respectively.

Based on a difference between the acceleration measured by IMU 8 a attached to revolving unit 2 and the acceleration measured by IMU 8 b attached to boom 3 a, an acceleration in extension and contraction of boom cylinder 4 a (an amount of change in speed of extension and contraction of boom cylinder 4 a) can be obtained.

Though boom angle θb, arm angle θa, and bucket angle θk are measured by the potentiometers in the present embodiment, they may be measured by the IMUS.

<Schematic Configuration of System of Work Machine>

A schematic configuration of a system of the work machine will now be described with reference to FIG. 2.

FIG. 2 is a block diagram showing a schematic configuration of a system of the work machine shown in FIG. 1. As shown in FIG. 2, the system in the present embodiment is a system for determining a payload value. The system in the present embodiment includes hydraulic excavator 100 representing an exemplary work machine shown in FIG. 1 and a controller 10 shown in FIG. 2. Controller 10 may be mounted on hydraulic excavator 100 or provided at a remote location distant from hydraulic excavator 100.

An operation apparatus 25 is arranged in operator's cab 2 a. Operation apparatus 25 is operated by an operator. Operation apparatus 25 accepts an operation by the operator for driving work implement 3. Operation apparatus 25 accepts an operation by the operator for revolving revolving unit 2. Operation apparatus 25 provides an operation signal in response to an operation by the operator. Though operation apparatus 25 is, for example, a pilot hydraulic operation apparatus in the present example, it may be an electrical operation apparatus.

A hydraulic pump 33 is driven by drive force from an engine 31. Hydraulic oil delivered from hydraulic pump 33 is supplied to operation apparatus 25. Hydraulic oil supplied to operation apparatus 25 is supplied to various hydraulic actuators 40 through a direction control valve 34 in correspondence with an operation onto operation apparatus 25 by the operator.

As supply and release of a hydraulic pressure to hydraulic actuator 40 is controlled, an operation of work implement 3, revolution of revolving unit 2, and a traveling operation of travel unit 1 are controlled. Hydraulic actuator 40 includes boom cylinder 4 a, arm cylinder 4 b, and bucket cylinder 4 c shown in FIG. 1 and a not-shown revolution motor.

Engine 31 is, for example, a diesel engine. Output from engine 31 is controlled by control of an amount of injection of fuel into engine 31 by controller 10.

Hydraulic pump 33 is coupled to engine 31. As rotational drive force from engine 31 is transmitted to hydraulic pump 33, hydraulic pump 33 is driven.

Hydraulic pump 33 is a variable displacement hydraulic pump that includes, for example, a swash plate and varies a delivery capacity as an angle of tilt of the swash plate is varied. Hydraulic oil delivered from hydraulic pump 33 is supplied to direction control valve 34 as being reduced in pressure to a certain pressure by a pressure reduction valve.

Direction control valve 34 is a spool type valve that switches a direction of flow of hydraulic oil, for example, by moving a rod-shaped spool. As the spool moves in an axial direction, an amount of supply of hydraulic oil to hydraulic actuator 40 is regulated. Direction control valve 34 is provided with a spool stroke sensor that detects a distance of movement of the spool (spool stroke).

In the present example, oil supplied to hydraulic actuator 40 for activating hydraulic actuator 40 is referred to as hydraulic oil. Oil supplied to direction control valve 34 for activating direction control valve 34 is referred to as pilot oil. A pressure of pilot oil is referred to as a PPC pressure (pilot hydraulic pressure).

Hydraulic pump 33 may deliver both of hydraulic oil and pilot oil. For example, some of hydraulic oil delivered from hydraulic pump 33 may be reduced in pressure by the pressure reduction valve and hydraulic oil reduced in pressure may be used as pilot oil. Hydraulic pump 33 may separately include a hydraulic pump (a main hydraulic pump) that delivers hydraulic oil and a hydraulic pump (pilot hydraulic pump) that delivers pilot oil.

Operation apparatus 25 includes a first control lever 25R and a second control lever 25L. First control lever 25R is arranged, for example, on the right of operator's seat 2 b. Second control lever 25L is arranged, for example, on the left of operator's seat 2 b. Operations in front, rear, left, and right directions onto first control lever 25R and second control lever 25L correspond to biaxial operations.

For example, boom 3 a and bucket 3 c are operated by operating first control lever 25R. An operation onto first control lever 25R in the fore/aft direction corresponds, for example, to an operation of boom 3 a, and an operation to raise boom 3 a and an operation to lower boom 3 a are performed in accordance with the operation in the fore/aft direction. An operation onto first control lever 25R in the lateral direction corresponds, for example, to an operation of bucket 3 c, and an operation in the upward/downward direction of bucket 3 c is performed in accordance with the operation in the lateral direction.

For example, arm 3 b and revolving unit 2 are operated by operating second control lever 25L. An operation in the fore/aft direction onto second control lever 25L corresponds, for example, to an operation of arm 3 b, and the operation of arm 3 b in the upward/downward direction is performed in accordance with the operation in the fore/aft direction. An operation onto second control lever 25L in the lateral direction corresponds, for example, revolution of revolving unit 2, and a right revolution operation and a left revolution operation of revolving unit 2 are performed in accordance with an operation in the lateral direction.

In the present example, an operation to raise boom 3 a is also referred to as a raising operation and an operation to lower boom 3 a is also referred to as a lowering operation. Operations of arm 3 b in the upward/downward direction are also referred to as a dumping operation and an excavation operation, respectively. Operations of bucket 3 c in the upward/downward direction are also referred to as a dumping operation and an excavation operation, respectively.

The operations in the lateral direction onto first control lever 25R may correspond to the operation of boom 3 a and the operation in the fore/aft direction may correspond to the operation of bucket 3 c. The fore/aft direction of second control lever 25L may correspond to the operation of revolving unit 2 and the operation in the lateral direction may correspond to the operation of arm 3 b.

Pilot oil delivered from hydraulic pump 33 and reduced in pressure by the pressure reduction valve is supplied to operation apparatus 25.

Operation apparatus 25 and direction control valve 34 are connected to each other through a pilot oil channel 450. A PPC pressure is regulated based on contents of an operation onto operation apparatus 25. As operation apparatus 25 is operated, a PPC pressure corresponding to the contents of operation onto operation apparatus 25 is supplied to direction control valve 34 through pilot oil channel 450. Direction control valve 34 is thus regulated to regulate a direction of flow and a flow rate of hydraulic oil supplied to boom cylinder 4 a, arm cylinder 4 b, and bucket cylinder 4 c, so that operations in the upward/downward direction of boom 3 a, arm 3 b, and bucket 3 c are performed.

A pressure sensor 36 is arranged in pilot oil channel 450. Pressure sensor 36 detects a PPC pressure. A result of detection by pressure sensor 36 is provided to controller 10. The PPC pressure regulated by an operation onto operation apparatus 25 and detected by pressure sensor 36 corresponds to an operation command value in the present embodiment.

Though shown in a simplified manner in FIG. 2, a plurality of pilot oil channels 450 corresponding to operations in fore/aft and lateral directions onto first control lever 25R and second control lever 25L are provided to connect operation apparatus 25 and direction control valve 34 to each other. Pressure sensor 36 is provided in each of the plurality of pilot oil channels 450.

For example, when boom 3 a is operated, pressure sensor 36 that detects increase in PPC pressure in the operation to raise boom 3 a is different from pressure sensor 36 that detects increase in PPC pressure in the operation to lower boom 3 a. For example, pressure sensor 36 that detects increase in PPC pressure in the dumping operation by arm 3 b is different from pressure sensor 36 that detects increase in PPC pressure in the excavation operation by arm 3 b. For example, when bucket 3 c is operated, pressure sensor 36 that detects increase in PPC pressure in the dumping operation by bucket 3 c is different from pressure sensor 36 that detects increase in PPC pressure in the excavation operation by bucket 3 c.

An amount of increase in PPC pressure is different depending on an angle of tilt of each of control levers 25L and 25R from a neutral position. Thus, contents of the operation onto operation apparatus 25 can be determined based on a result of detection of the PPC pressure by each pressure sensor 36.

Detection signals from stroke sensors 7 a to 7 c, IMUs 8 a to 8 d, potentiometers 9 a to 9 c, and pressure sensors 6 a and 6 b are also provided to controller 10.

Controller 10 may electrically be connected to each of stroke sensors 7 a to 7 c, IMUs 8 a to 8 d, potentiometers 9 a to 9 c, and pressure sensors 6 a, 6 b, and 36 through wires, or may wirelessly communicate therewith. Controller 10 may be implemented, for example, by a computer, a server, or a portable terminal, or by a central processing unit (CPU).

<Functional Block in Controller 10>

A functional block in controller 10 will now be described with reference to FIG. 3.

FIG. 3 is a diagram showing a functional block within the controller shown in FIG. 2. As shown in FIG. 3, controller 10 includes an operation command value obtaining unit 11, a boom cylinder extension and contraction speed obtaining unit 12, a payload calculation value arithmetic unit 13, a storage 14, a change amount obtaining unit 15, a weight calculator 16, a weight ranking unit 17, and a payload value determination unit 18.

Operation command value obtaining unit 11 receives input of a signal indicating a PPC pressure detected by pressure sensor 36. Operation command value obtaining unit 11 detects, for example, an operation command value for operating boom cylinder 4 a from the signal indicating the PPC pressure detected by pressure sensor 36. The operation command value obtained by operation command value obtaining unit 11 is provided to storage 14 and stored therein.

Boom cylinder extension and contraction speed obtaining unit 12 receives input of a signal indicating an acceleration or the like detected by each of IMUs 8 a to 8 d. Boom cylinder extension and contraction speed obtaining unit 12 detects an acceleration in extension and contraction of boom cylinder 4 a (an amount of change in speed of extension and contraction of boom cylinder 4 a), for example, based on a difference between the acceleration detected by IMU 8 a attached to revolving unit 2 and the acceleration detected by IMU 8 b attached to boom 3 a.

Boom cylinder extension and contraction speed obtaining unit 12 receives input of signals indicating amounts of displacement of the cylinder rods or angles of the work implement (boom angle θb, arm angle θa, and bucket angle θk) detected by stroke sensors 7 a to 7 c. Boom cylinder extension and contraction speed obtaining unit 12 detects a speed of extension and contraction of boom cylinder 4 a, for example, based on an amount of displacement of the cylinder rod or an angle of the work implement (boom angle θb) detected by stroke sensor 7 a.

Boom cylinder extension and contraction speed obtaining unit 12 receives input of signals indicating angles of the work implement (boom angle θb, arm angle θa, and bucket angle θk) detected by potentiometers 9 a to 9 c. Boom cylinder extension and contraction speed obtaining unit 12 detects a speed of extension and contraction of boom cylinder 4 a, for example, based on an angle of the work implement (boom angle θb) detected by potentiometer 9 a.

The speed of extension and contraction (or the amount of change in speed of extension and contraction) of boom cylinder 4 a detected by boom cylinder extension and contraction speed obtaining unit 12 is provided to storage 14 and stored therein.

Payload calculation value arithmetic unit 13 receives input of signals indicating a head pressure and a bottom pressure of boom cylinder 4 a detected by pressure sensors 6 a and 6 b. Payload calculation value arithmetic unit 13 receives input of signals indicating amounts of displacement of the cylinder rods or angles of the work implement (boom angle θb, arm angle θa, and bucket angle θk) detected by stroke sensors 7 a to 7 c. Payload calculation value arithmetic unit 13 receives input of signals indicating angles of the work implement (boom angle θb, arm angle θa, and bucket angle θk) detected by potentiometers 9 a to 9 c.

Payload calculation value arithmetic unit 13 calculates a payload calculation value from the provided signal. The payload calculation value calculated by payload calculation value arithmetic unit 13 is transmitted to storage 14 and stored therein.

Change amount obtaining unit 15 obtains an amount of change per unit time in information on at least one of the operation command value for operating boom cylinder 4 a and the speed of extension and contraction of boom cylinder 4 a, from information stored in storage 14.

Change amount obtaining unit 15 obtains the amount of change per unit time in operation command value for operating boom cylinder 4 a, for example, from the signal indicating the PPC pressure obtained by operation command value obtaining unit 11 and stored in storage 14.

Change amount obtaining unit 15 obtains the amount of change per unit time in speed of extension and contraction of boom cylinder 4 a, for example, from the amount of change in speed of extension and contraction of boom cylinder 4 a obtained by operation command value obtaining unit 11 and stored in storage 14.

Change amount obtaining unit 15 obtains the amount of change per unit time in speed of extension and contraction of boom cylinder 4 a, for example, from the speed of extension and contraction of boom cylinder 4 a obtained by operation command value obtaining unit 11 and stored in storage 14.

The amount of change obtained by change amount obtaining unit 15 is provided to weight calculator 16. Weight calculator 16 calculates a weight (a weighted value) to be used for weighted average based on the amount of change provided from change amount obtaining unit 15. The weight calculated by weight calculator 16 is provided to storage 14 and stored therein.

Weight ranking unit 17 ranks a plurality of weights stored in storage 14 based on magnitude of the weights.

Payload value determination unit 18 determines a payload value by weighted average, based on the payload calculation values and the weights stored in storage 14. When a calculation section is long (for example, not shorter than three seconds), payload value determination unit 18 may determine the payload value by weighted average using only data large in weight among the weights ranked by weight ranking unit 17 (that is, rather than data small in weight). In the present embodiment, the payload value may be determined by weighted average using only N pieces of data large in weight ranked by weight ranking unit 17.

<Method of Controlling Work Machine>

A method of controlling the work machine in the present embodiment will now be described with reference to FIGS. 3 and 4.

FIG. 4 is a flowchart showing a method of controlling the work machine in one embodiment of the present disclosure. As shown in FIG. 4, in the present embodiment, initially, a current payload calculation value (CalcuPayload) of a load within bucket 3 c is calculated (step S1). This payload calculation value (CalcuPayload) is calculated based on static balance. Specifically, after a moment MX_(we) caused by self-weight of work implement 3 is calculated, a current payload calculation value of a load within bucket 3 c is calculated based on balance of moments around boom foot pin 5 a. The payload calculation value (CalcuPayload) is calculated by payload calculation value arithmetic unit 13 shown in FIG. 3.

Initially, moment MX_(we) caused by self-weight of work implement 3 is calculated in accordance with an expression (1) below.

$\begin{matrix} {\mspace{79mu}\left\lbrack {{Expression}\mspace{14mu} 1} \right\rbrack} & \; \\ {{MX}_{we} = {{M_{boom} \times X_{{boom}\;\_\; c}} + {M_{boomC} \times X_{{boomC}\;\_\; c}} + {M_{boomCR} \times X_{{boomCR}\;\_\; c}} + {M_{arm} \times X_{{arm}\;\_\; c}} + {M_{armC} \times X_{{armC}\;\_\; c}} + {M_{armCR} \times X_{{armCR}\;\_\; c}} + {M_{bucket} \times X_{{bucket}\;\_\; c}}}} & (1) \end{matrix}$

In the expression (1), M_(boom) represents a weight of boom 3 a. M_(boomC) represents a weight of a cylinder portion of boom cylinder 4 a. M_(boomCR) represents a weight of a cylinder rod portion of boom cylinder 4 a. M_(arm) represents a weight of arm 3 b. M_(armC) represents a weight of a cylinder portion of arm cylinder 4 b. M_(armCR) represents a weight of a cylinder rod portion of arm cylinder 4 b. M_(bucket) represents a weight of bucket 3 c.

Each of weights M_(boom), M_(boomC), M_(boomCR), M_(arm), M_(armC), M_(armCR), and M_(bucket) is stored in storage 14, for example, by an operation for input to storage 14 onto input operation portion 21 as shown in FIG. 3.

In the expression (1), X_(boom_c) represents a distance from boom foot pin 5 a to the center of gravity of boom 3 a. X_(boomC_c) represents a distance from boom foot pin 5 a to the center of gravity of the cylinder portion of boom cylinder 4 a. X_(boomCR_c) represents a distance from boom foot pin 5 a to the cylinder rod portion of boom cylinder 4 a. X_(arm_c) represents a distance from boom foot pin 5 a to the center of gravity of arm 3 b. X_(armc_c) represents a distance from boom foot pin 5 a to the center of gravity of the cylinder portion of arm cylinder 4 b. X_(armCR_c) represents a distance from boom foot pin 5 a to the center of gravity of the cylinder rod portion of arm cylinder 4 b. X_(bucket_c) represents a distance from boom foot pin 5 a to the center of gravity of bucket 3 c.

Each of these distances X_(boom_c), X_(boomC_c), X_(boomCR_c), X_(arm_c), X_(armC_c), X_(armCR_c), and X_(bucket) can be calculated from results of detection by stroke sensors 7 a to 7 c and potentiometers 9 a to 9 c.

Moment MX_(we) is calculated by payload calculation value arithmetic unit 13 shown in FIG. 3.

Balance of moments around boom foot pin 5 a is expressed in an expression (2) below.

[Expression 2]

F×h=CalcuPayload×X _(payload_c) +MX _(we)  (2)

In the expression (2), F represents load (pressing force) of boom cylinder 4 a and it is obtained from a head pressure and a bottom pressure of boom cylinder 4 a. Therefore, F is obtained from a pressure (head pressure) detected by pressure sensor 6 a and a pressure (bottom pressure) detected by pressure sensor 6 b.

In the expression (2), h represents a shortest distance between boom foot pin 5 a and boom cylinder 4 a (a distance in a direction orthogonal to a direction of extension of boom cylinder 4 a). h can be calculated from detection values from stroke sensor 7 a and potentiometer 9 a.

In the expression (2), X_(payload_c) represents a distance between boom foot pin 5 a and the center of gravity of a load within bucket 3 c. X_(payload_c) can be calculated from detection values from stroke sensors 7 a to 7 c and potentiometers 9 a to 9 c.

Based on the expression (2), a payload calculation value (CalcuPayload) is expressed in an expression (3) below.

$\begin{matrix} \left\lbrack {{Expression}\mspace{14mu} 3} \right\rbrack & \; \\ {{CalcuPayload} = \frac{{F \times h} - {MX}_{we}}{X_{{payload}\;\_\; c}}} & (3) \end{matrix}$

As shown in the expression (3), the payload calculation value (CalcuPayload) of a load within bucket 3 c is calculated based on load F of boom cylinder 4 a. The payload calculation value is constantly calculated.

Then, whether or not an operation to raise boom 3 a is being performed is determined (step S2: FIG. 4). For example, when the operation to raise boom 3 a and the operation to revolve revolving unit 2 are simultaneously being performed, it may be determined that the operation to raise boom 3 a is being performed. Whether or not the operation to raise boom 3 a and the operation to revolve revolving unit 2 are being performed may be determined, for example, by detection of a PPC pressure by pressure sensor 36.

When it is determined that the operation to raise boom 3 a is not being performed, calculation of the payload calculation value (CalcuPayload) is continued. When it is determined that the operation to raise boom 3 a is being performed, the amount of change in boom raising PPC pressure per unit time is calculated (step S3: FIG. 4).

In calculating the amount of change, an amount of change X in boom raising PPC pressure per unit time is calculated based on the boom raising PPC pressure at a first time point before the moment of calculation of the payload calculation value and the boom raising PPC pressure at a second time point before the first time point.

As set forth above, amount of change X per unit time in operation command value (boom raising PPC pressure) for operating boom cylinder 4 a is detected. Detection by calculation of amount of change X is done by change amount obtaining unit 15 shown in FIG. 3.

The payload calculation value (CalcuPayload) obtained in calculation above is corrected based on thus detected amount of change X per unit time, to thereby determine a payload value W_(payload) (step S4: FIG. 4). In correction of the payload calculation value, initially, a weight (weighted value) W is calculated based on amount of change X (step S4 a).

Weight W is calculated, for example, from a reciprocal of amount of change X. Thus, weight W at the time when amount of change X per unit time is large is small, whereas weight W at the time when amount of change X per unit time is small is large. Weight W is calculated by weight calculator 16 shown in FIG. 3.

Amount of change X per unit time and weight W are constantly calculated, and weight W calculated at each moment is stored in storage 14 shown in FIG. 3.

Then, weights W stored in storage 14 are ranked (step S4 b). Weights W are ranked in the order of magnitude of weight W. Weights W are ranked by weight ranking unit 17 shown in FIG. 3.

Then, payload value W_(payload) is determined by weighted average of the payload calculation values (CalcuPayload) using weight W obtained above (step S4 c: FIG. 4). In determining payload value W_(payload), an expression (4) below is used.

$\begin{matrix} {\mspace{79mu}\left\lbrack {{Expression}\mspace{20mu} 4} \right\rbrack} & \; \\ {{WPayload} = \frac{\begin{matrix} {{W_{1} \times {{Calcupayload}\;}_{1}} + {W_{2} \times {{Calcupayload}\;}_{2}} +} \\ {{W_{3} \times {{Calcupayload}\;}_{3}} + \ldots + {W_{t} \times {{Calcupayload}\;}_{t}}} \end{matrix}}{W_{1} + W_{2} + W_{3} + \ldots + W_{t}}} & (4) \end{matrix}$

In the expression (4), CalcuPayload₁, CalcuPayload₂, CalcuPayload₃, and CalcuPayload_(t) represent payload calculation values obtained as above at respective time points 1, 2, 3, and t. W₁, W₂, W₃, and W_(t) represent weights obtained as above at respective time points 1, 2, 3, and t.

As shown in the expression (4), the weighted average of the payload calculation values is calculated, with the weight at the time when the amount of change per unit time is large being made smaller and with the weight at the time when the amount of change per unit time is small being made larger. Payload value W_(payload) is determined by payload value determination unit 18 shown in FIG. 3.

In the present embodiment, the payload value may be determined by the weighted average shown in the expression (4), using only data of top thirty weights larger in weight (the weight and the payload calculation value corresponding to the weight), rather than data of a plurality of weights smaller in weight (the weight and the payload calculation value corresponding to the weight) among the plurality of weights ranked by weight ranking unit 17.

As the payload calculation value (CalcuPayload) is corrected based on amount of change X per unit time as set forth above, payload value W_(payload) is determined.

Determined payload value W_(payload) is corrected for eliminating an error that the individual work machine has (step S5: FIG. 4). The payload value is corrected by determining payload value W_(payload) as above while there is no load in bucket 3 c (an unloaded state) and subtracting payload value W_(payload) in the unloaded state from payload value W_(payload) obtained while there is a load within bucket 3 c. As a result of correction, a difference in kinetic friction or resistance caused by individual variation among work machines can be canceled.

Thereafter, whether or not the load has been removed from bucket 3 c is determined (step S6: FIG. 4). The load is removed from bucket 3 c, for example, for loading the load onto a dump truck.

When it is determined that the load has not been removed from bucket 3 c, the payload calculation value is calculated again (step S1: FIG. 4). When it is determined that the load has been removed from bucket 3 c, the corrected payload value is finalized, and the finalized corrected payload value is added to a carrying capacity of the dump truck (step S7: FIG. 4).

The corrected payload value and the carrying capacity of the dump truck are shown, for example, on a display within operator's cab 2 a. An operator in operator's cab 2 a can thus perform excavation and loading works while the operator checks the corrected payload value of the load within bucket 3 c and the carrying capacity of the dump truck.

As set forth above, the payload value of the load within bucket 3 c is determined and added to the carrying capacity of the dump truck.

Though the case of pilot hydraulic operation apparatus 25 is described above, electrical operation apparatus 25 may be applicable. When electrical operation apparatus 25 is provided, an amount of operation onto each of first control lever 25R and second control lever 25L is detected, for example, by a potentiometer. The potentiometer refers to a displacement sensor that obtains an electrical (voltage) output in proportion to a mechanical position. Therefore, an amount of change per unit time in electrical (voltage) output obtained from the potentiometer as the amount of change per unit time in operation command value may be used for calculating weight W for weighted average.

Though an example of weighted average by calculating a weight based on amount of change X per unit time in operation command value is described above, weighted average may be calculated by calculating a weight based on the amount of change per unit time in speed of extension and contraction of the boom cylinder. Alternatively, weighted average may be calculated by calculating a weight based on both of amount of change X per unit time in operation command value and the amount of change per unit time in speed of extension and contraction of the boom cylinder.

Functions and Effects

Functions and effects of the present embodiment will now be described together with findings made by the present inventors as shown in FIG. 5.

FIG. 5 is a diagram showing change over time in boom raising PPC pressure, amount of change in boom raising PPC pressure, and payload calculation value (CalcuPayload). As shown in FIG. 5, the present inventors have found that, in the operation to raise boom 3 a in which the PPC pressure (a solid line in the figure) of boom 3 a increases, the amount of change in PPC pressure of boom 3 a pulsates with an operation onto boom 3 a, and with pulsation, the payload calculation value (CalcuPayload) also pulsates. It is thus found difficult to accurately measure a load within bucket 3 c in the operation to raise boom 3 a.

The present inventors have also found that accuracy of the payload calculation value (CalcuPayload) is poorer when the speed of raising boom 3 a is high. Therefore, the operation to raise boom 3 a should carefully be performed. When the operation to raise boom 3 a is carefully performed, however, productivity becomes poor.

Then, in the present embodiment, payload value W_(payload) is determined by correcting the payload calculation value (CalcuPayload) based on the amount of change per unit time in information on at least one of the operation command value for operating boom cylinder 4 a and the speed of extension and contraction of boom cylinder 4 a. Thus, payload value W_(payload) less in pulsation in the payload calculation value (CalcuPayload) in the operation of boom 3 a can be obtained. Therefore, the load within bucket 3 c can accurately be measured in the operation of boom 3 a. Therefore, the operator can accurately measure the load within bucket 3 c simply by performing operations as usual, and high productivity can also be maintained.

According to the present embodiment, payload value W_(payload) is determined by weighted average of the payload calculation values (CalcuPayload), with weight W at the time when amount of change X per unit time is large being made smaller and with weight W at the time when amount of change X per unit time is small being made larger. By thus increasing weight W at the time when amount of change X is small, a result of calculation can be stabilized.

Payload value W_(payload) is determined by calculating an average rather than by using an instantaneous measurement value. Therefore, even when the head pressure and the bottom pressure of boom cylinder 4 a are disturbed like noise due to a sudden operation, such disturbance does not greatly affect a measurement result.

According to the present embodiment, a plurality of weights are calculated, and payload value W_(payload) is determined by calculating weighted average using payload calculation values large in weight among the plurality of weights, rather than payload calculation values small in weight among the plurality of weights. Thus, even when a calculation section is, for example, as short as three seconds, stable payload value W_(payload) can be calculated.

According to the present embodiment, the operation command value and the speed of extension and contraction of boom cylinder 4 a are the operation command value and the speed of extension and contraction of boom cylinder 4 a at the time when the operation to raise boom 3 a is performed. Thus, payload value W_(payload) less in pulsation in the payload calculation value (CalcuPayload) at the time when the operation to raise boom 3 a is performed can be obtained.

It should be understood that the embodiment disclosed herein is illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims rather than the description above and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

REFERENCE SIGNS LIST

-   -   1 travel unit; 1 a crawler belt apparatus; 2 revolving unit; 2 a         operator's cab; 2 b operator's seat; 2 c engine compartment; 2 d         counterweight; 3 work implement; 3 a boom; 3 b arm; 3 c bucket;         3 d bucket link; 3 da first link member; 3 db second link         member; 3 dc bucket cylinder top pin; 3 dd first link pin; 3 de         second link pin; 4 a boom cylinder; 4 aa cylinder; 4 ab cylinder         rod; 4 b arm cylinder; 4 c bucket cylinder; 5 a boom foot pin; 5         b boom tip end pin; 5 c pin; 6 a, 6 b, 36 pressure sensor; 7 a,         7 b, 7 c stroke sensor; 8 a, 8 b, 8 c IMU; 9 a, 9 b, 9 c         potentiometer; 10 controller; 11 operation command value         obtaining unit; 12 boom cylinder extension and contraction speed         obtaining unit; 13 payload calculation value arithmetic unit; 14         storage; 15 change amount obtaining unit; 16 weight calculator;         17 weight ranking unit; 18 payload value determination unit; 21         input operation portion; 25 operation apparatus; 25L second         control lever; 25R first control lever; 31 engine; 33 hydraulic         pump; 34 direction control valve; 40 hydraulic actuator; 100         hydraulic excavator; 450 pilot oil channel 

1. A work machine comprising: a boom; an arm attached to a tip end of the boom; a bucket attached to a tip end of the arm; a boom cylinder that drives the boom; and a controller that calculates a payload calculation value of a load within the bucket based on load of the boom cylinder, detects an amount of change per unit time in information on at least one of an operation command value for operating the boom cylinder and a speed of extension and contraction of the boom cylinder, and determines a payload value by correcting based on the amount of change per unit time, the payload calculation value obtained by calculation.
 2. The work machine according to claim 1, wherein the controller determines the payload value by calculating a weighted average of payload calculation values with a weight at time when the amount of change per unit time is large being made smaller and with a weight at time when the amount of change per unit time is small being made larger.
 3. The work machine according to claim 2, wherein the controller calculates a plurality of weights, and determines the payload value by calculating the weighted average of the payload calculation values large in weight among the plurality of weights, rather than the payload calculation values small in weight among the plurality of weights.
 4. The work machine according to claim 1, wherein the operation command value and the speed of extension and contraction of the boom cylinder refer to the operation command value and the speed of extension and contraction of the boom cylinder in an operation to raise the boom, respectively.
 5. A system comprising: a work machine including a boom, an arm attached to a tip end of the boom, a bucket attached to a tip end of the arm, and a boom cylinder that drives the boom; and a controller that obtains an amount of change per unit time in information on at least one of an operation command value for operating the boom cylinder and a speed of extension and contraction of the boom cylinder, calculates a payload calculation value of a load within the bucket based on load of the boom cylinder, and determines a payload value by correcting based on the amount of change per unit time, the payload calculation value obtained by calculation.
 6. A method of controlling a work machine, the work machine including a boom, an arm attached to a tip end of the boom, a bucket attached to a tip end of the arm, and a boom cylinder that drives the boom, the method comprising: calculating a payload calculation value of a load within the bucket based on load of the boom cylinder; and obtaining an amount of change per unit time in information on at least one of an operation command value for operating the boom cylinder and a speed of extension and contraction of the boom cylinder and determining a payload value by correcting based on the amount of change per unit time, the payload calculation value obtained by calculation. 